The country's Court of Appeal on Thursday rejected a request by the German-born tech mogul to overturn a decision allowing his extradition.

Now, more than six years into the saga, his lawyers say they will take the matter to New Zealand's top judicial body, the Supreme Court.

"To say that I am extremely disappointed by the decision ... is an understatement," Dotcom said in a statement.

The Megaupload founder and his three co-accused - Mathias Ortmann, Bran van der Kolk and Finn Botato - were arrested in 2012 in a dramatic police raid and charged with a series of copyright-related offences on behalf of authorities in the US over their roles in running the file-sharing website.

"The evidence relied on by the United States discloses a clear prima facie case to support the allegations that the appellants conspired to, and did, breach copyright wilfully and on a massive scale for commercial gain," a summary of the Court of Appeal's judgement said.

The three judges also rejected questions about misconduct by the United States in the case, saying it was "not of sufficient importance to warrant a further appeal" and overturned an earlier decision ruling out New Zealand's copyright laws as grounds for extradition.

"The court's interpretation of the relevant copyright provisions cannot be right," Dotcom said.

"My legal team are confident that the Supreme Court will hear the appeal, given there are such significant legal issues at stake."

If that final bid does fail, the ultimate decision will then rest with New Zealand's Justice Minister, Andrew Little.

"One thing I won't be doing is predetermining that decision," Mr Little told reporters in Wellington on Thursday.

"Until he has exhausted all his legal appeals and legal process there is nothing for me to do."

The US Federal Bureau of Investigation has led the case and claims Megaupload was a criminal conspiracy that earned the men $US175 million ($A237 million).

It's been touted as one of the largest criminal copyright cases ever and if extradited and found guilty in the US, the quartet could face decades in jail.

Australian Associated Press